The present invention relates to a looper thread paying-out apparatus in a sewing machine for feeding a thread from a bobbin through a thread tensioner to seam forming means.
In the prior sewing machine a paying-out of thread from a bobbin has been carried out by a thread take-up arranged between a thread tensioner and the seam forming means such as a needle or looper. At the same time with this paying-out of thread by the thread take-up a stitch is further fastened.
Therefore, in the case of a bobbin in which a thread paying-out tension was easily variable there was a problem that an amount of thread paid out by the thread take-up was not constant resulting in a non-uniform seam because the amount of thread paid out by the thread take-up must be set up in consideration of the thread paying-out tension.
For example, in the case of multi-thread chain stitch in an interlock sewing machine, it has a problem that a stitch is varied depending on a thread paying-out tension in such a way that upon a lower thread paying-out tension the stitch as shown in FIG. 7(A) is obtained and upon a higher thread paying-out tension a stitch as shown in FIG. 7(B) is obtained.
In particular, such a variation of stitch is found noticeably at an intermittent sewing or at a transfer of sewing speed from a lower speed to a higher speed so that it was very difficult to control an amount of thread paid out by a thread take-up and an amount of thread paying-out by a spring pressure of thread tensioner.